Preservation of hematopoietic stem/progenitor cells (HSPC) is conventionally carried out using low temperature freezing either at −80° C. (mechanical freezers) or at −196° C. (liquid nitrogen) and it is altogether a separate science in itself. Present invention relates to maintenance of HSC in culture. Maintenance HSPC in vitro without proliferation or differentiation has important clinical applications. Techniques such as in vitro purging of tumor cells using culture techniques or by use of chemotherapeutic agents necessitates that the HSPC remain unaffected in the culture. In genetic engineering protocols it could be advantageous to eliminate all the short-lived progenitors, which are growth factor dependent and then use the surviving primitive cells for transduction purposes. Thus a search for agents which can maintain the HSPC in culture and identification of signals involved in maintenance of the quiescent state is likely to form a fruitful endeavor. Earlier efforts in this direction to maintain HSPC in culture have been made using either specific matrix molecules like denatured collagen (Mauney et al, 2004 Biomaterials, 25, 16: 3233-43; Kim et al 2003, Int J Hematol; 78, 2:126-32; Banu et al 2001, Cytokine. 21; 13, 6:349-58) or growth factors like FLT3L (Shapiro et al 1996, Hematother; 5, 6:655-62) or hematopoietic growth factors like Epo (Eridani et al 1998, Biotherapy 10, 4:295-8). These approaches, however, involve use of expensive reagents. The cost factor becomes a major issue when it is to be applied to clinical set ups especially in developing countries. Recently, a lectin named Flt3 receptor-interacting lectin (FRIL) was shown to preserve the quiescent HSPC derived from cord blood (CB) in culture for 30 days without the change of medium and without the exogenous addition of growth factors. (Colucci, G. et al 1999 Proc. Natl. Acad. Sci. USA 96, 646-650; Kollet O. et al 2000 Expt. Hematol. 28, 726-736.) The plant lectin FRIL was shown to support prolonged in vitro maintenance of quiescent, human cord blood CD 34 (+) CD38 (−/low)/SCID repopulating stem cells. It is reported that this maintenance of quiescent CB progenitors may be through the cell cycle modulation through HTm4 and HTm4S (Xie, X. Y., Xie C., Shi, W., Li, J., Li, Y. H., Wang, D. M., Bai, C. X., Chen, L. & Pei, X. T. 2004 56, 306-312).
Since FRIL is a mannose binding lectin, screening for more mannose binding lectins have been done for their possible HSPC preservation activity so that they can also be used as tools to identify the signals involved in maintenance of quiescent HSPC. Thus the present invention has two distinct advantages over earlier approaches, one of being cost effective and the second of providing useful and specific reagents to study signaling mechanisms.
Maintenance of HSPC in culture has a great clinical utility especially if it can be done without change of medium or use of expensive reagents. The present invention provides a method to achieve this. The mannose specific lectins that have been used in the present study showed HSPC preservation activity up to 30 days without growth factor addition or medium change providing a cost effective method to preserve HSPC in culture.